It's a really personal decision but I told my work team immediately after confirmation of diagnosis and it was a good move. I knew I would have chemo, I wanted to work through if I could and I felt it would all go better if we just got it dealt with at the start. But it has to be something you feel really comfortable about. I'd worked with someone who had done the same thing, and wasn't too worried about the responses. If and when you do tell, let them know what you want. I didn't want sympathy or special treatment (other than TELL me if I am getting chemo brain - they would have and I didn't!) and established that jokes etc were welcome. That way peole don't get all awkward and add to the things you have to cope with unintentionally. Best wishes.